Standard MBean

MBeanServer mbs = ...something...;
ObjectName name =
    new ObjectName("com.example:type=Memory");
MemoryMBean proxy =
     JMX.newMBeanProxy(mbs, name, MemoryMBean.class);
MemoryUsage memoryUsage = proxy.getMemoryUsage();
Long used = memoryUsage.getUsed();

MXBean

MBeanServer mbs = ...something...;
ObjectName name =
    new ObjectName("com.example:type=Memory");
MemoryMXBean proxy =
     JMX.newMXBeanProxy(mbs, name, MemoryMXBean.class);
MemoryUsage memoryUsage = proxy.getMemoryUsage();
long used = memoryUsage.getUsed();